1. Field of the Technology
The present invention relates generally to a cathode ray tube, and particularly concerns a cathode ray tube apparatus of high resolution power suitable for displaying graphic and Chinese character displaying.
2. Description of the Prior Art
Cathode ray tubes for use in graphic displaying or Chinese character displaying requires specially high resolution power. Hitherto, raising of anode potential or enlarging diameter of electron gun have been tried for improving the resolution. However, the former induces undesirable radiation of x-ray emission and the latter results in increase of deflection power, resulting in high cost.
Published Japanese Unexamined Application No. Sho 57-30247 discloses a cathode ray tube apparatus, wherein an electron beam crosses the axis of the electron gun twice, firstly at a region of a prefocus lens, and secondly before incidence to a main lens. Spherical aberration at the main lens is thus decreased, resulting in a high resolution. The above-mentioned application has a problem that, while a high resolution is obtainable for a high electron beam operation, in a low electron beam operation for a low luminance displaying the improvement of resolution is not achieved but rather induces poor resolution since electron beam only from circumference part of the emitting face 2 crosses the electron gun axis twice.